Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock

On Wed, Oct 25, 2023 at 10:34 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Oct 24, 2023 at 9:34 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:

> Overall I agree with your comments, actually, I haven't put that much
> thought into the GUC part and how it scales the SLRU buffers w.r.t.
> this single configurable parameter. Yeah, so I think it is better
> that we take the older patch version as our base patch where we have
> separate GUC per SLRU.
>
> > I'm inclined to use Borodin's patch last posted here [2] instead of your
> > proposed 0001.
> > [2] https://postgr.es/m/93236D36-B91C-4DFA-AF03-99C083840378@yandex-team.ru
>
> I will rebase my patches on top of this.

I have taken 0001 and 0002 from [1], done some bug fixes in 0001, and
changed the logic of SlruAdjustNSlots() in 0002, such that now it
starts with the next power of 2 value of the configured slots and
keeps doubling the number of banks until we reach the number of banks
to the max SLRU_MAX_BANKS(128) and bank size is bigger than
SLRU_MIN_BANK_SIZE (8). By doing so, we will ensure we don't have too
many banks, but also that we don't have very large banks. There was
also a patch 0003 in this thread but I haven't taken this as this is
another optimization of merging some structure members and I will
analyze the performance characteristic of this and try to add it on
top of the complete patch series.

Patch details:
0001 - GUC parameter for each SLRU
0002 - Divide the SLRU pool into banks
(The above 2 are taken from [1] with some modification and rebasing by me)
0003 - Implement bank-wise SLRU lock as described in the first email
of this thread
0004 - Implement bank-wise LRU counter as described in the first email
of this thread
0005 - Some other optimization suggested offlist by Alvaro, i.e.
merging buffer locks and bank locks in the same array so that the
bank-wise LRU counter does not fetch the next cache line in a hot
function SlruRecentlyUsed()

Note: I think 0003,0004 and 0005 can be merged together but kept
separate so that we can review them independently and see how useful
each of them is.

[1] https://postgr.es/m/93236D36-B91C-4DFA-AF03-99C083840378@yandex-team.ru

--
Regards,
Dilip Kumar
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